The couple Riho and her boyfriend, both working adults, move into a new home with marriage in mind. Riho, who was excited about their happy life together, had been troubled by her buttocks moving on their own as if they had another personality. She meets Okada, an impoverished student, at their new place. Concerned about Okada's unhealthy lifestyle, Riho starts bringing him meals and taking care of him since she works from home. Unsatisfied with the sex life with her boyfriend, Riho feels a throbbing in her buttocks while making lunch at Okada's place and ends up craving his cock.
